As Tom explains, toasters don't have timing chips - they have a bi-metallic strip: two pieces of metal, which heat up and expand at different rates, so the strip slowly begins to curl – the dial changes how far that strip has to curve before it triggers the component that makes the toast pop up.

Although, as one commentor has pointed out, more modern toasters use a capacitor charged by a variable resistor that switches off once it reaches a specific voltage.